In industrial applications where process parameters, such as pressure or flow, must be measured, excellent dc stability of the sensors and associated transducers is required in order to obtain accurate measurements. Because of this, the transducer utilized must exhibit extremely low output drift.
Fiber optic sensors and transducers have been used in industrial measurement applications, such as pressure measurement. It has been found that fiber optic sensors that measure changes in light intensity have better dc stability than sensors that measure changes in light phase or polarization. Fiber optic sensors that measure light intensity, however, have other operating characteristics which offset the foregoing better dc stability. For example, use of intensity sensors typically results in inherent measurement errors caused by cable and sensor lead bending and connector coupling loss. Because of this, some types of fiber optic sensors cannot be used in applications where low output drift is required while other types of fiber optic sensors require the utilization of techniques to compensate for changes in parameters other than the parameter being measured. Such compensation techniques typically increase system complexity and cost.
Because of the foregoing problems associated with the prior art apparatus and methods for measuring process parameters by utilizing fiber optic sensors, it has become desirable to develop a system and method for producing very accurate measurements of process parameters, such as pressure, in industrial applications.